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PubMed2003

Temporal variation in feeding morphology and size-structured population dynamics in fishes.

Considerable variation in morphology associated with resource use is a classic example of local adaptation to the environment. We demonstrate that a temporal change in feeding morphology might occur within a population. In a 5-year natural field experiment, we estimated gill raker morphology, resource density and population dynamics of the roach and its competitor, the perch. Despite a variation in density of zooplankton resources and perch across years, no change in roach density was observed. However, gill raker morphology in roach covaried with size structure of the zooplankton resource across years. A laboratory experiment confirmed that gill raker morphology has a great effect on roach foraging efficiency on zooplankton and that there is a functional trade-off with regard to zooplankton foraging. We suggest that the response in gill raker structure is an adaptation to deal with the rapid population dynamics of zooplankton, which are in turn mediated by changes in the size structure of the competing perch.

Adaptation, Physiological↗
PubMed2005

A structured-population model of Proteus mirabilis swarm-colony development.

In this paper we present continuous age- and space-structured models and numerical computations of Proteus mirabilis swarm-colony development. We base the mathematical representation of the cell-cycle dynamics of Proteus mirabilis on those developed by Esipov and Shapiro, which are the best understood aspects of the system, and we make minimum assumptions about less-understood mechanisms, such as precise forms of the spatial diffusion. The models in this paper have explicit age-structure and, when solved numerically, display both the temporal and spatial regularity seen in experiments, whereas the Esipov and Shapiro model, when solved accurately, shows only the temporal regularity. The composite hyperbolic-parabolic partial differential equations used to model Proteus mirabilis swarm-colony development are relevant to other biological systems where the spatial dynamics depend on local physiological structure. We use computational methods designed for such systems, with known convergence properties, to obtain the numerical results presented in this paper.

Agar↗
PubMed2006

Evolutionary aspects of population structure for molecular and quantitative traits in the freshwater snail Radix balthica.

Detecting the action of selection in natural populations can be achieved using the QST-FST comparison that relies on the estimation of FST with neutral markers, and QST using quantitative traits potentially under selection. QST higher than FST suggests the action of directional selection and thus potential local adaptation. In this article, we apply the QST-FST comparison to four populations of the hermaphroditic freshwater snail Radix balthica located in a floodplain habitat. In contrast to most studies published so far, we did not detect evidence of directional selection for local optima for any of the traits we measured: QST calculated using three different methods was never higher than FST. A strong inbreeding depression was also detected, indicating that outcrossing is probably predominant over selfing in the studied populations. Our results suggest that in this floodplain habitat, local adaptation of R. balthica populations may be hindered by genetic drift, and possibly altered by uneven gene flow linked to flood frequency.

Animals↗
PubMed1997

Mhc diversity in Pacific salmon: population structure and trans-species allelism.

Geographic variation at an Mhc class I A1 exon was surveyed in 14 populations of coho salmon (Oncorhynchus kisutch) and 15 populations of chinook salmon (O. tshawytscha) inhabiting rivers of British Columbia, Canada. A total of 2,504 fish were sampled using denaturing gradient gel electrophoresis (DGGE), which distinguished 17 alleles in coho salmon and 20 alleles in chinook salmon. Heterozygosity at the A1 locus was moderately high for both coho (0.7) and chinook (0.6) salmon, but sequence divergence was low, with mean inter- and intraspecific nucleotide similarities of approximately 0.96. In a maximum parsimony tree, all of the observed alleles clustered into two trans-specific lineages. Within each lineage, coho and chinook alleles tended to fall into species-specific subclusters. Much of the intraspecific allelic variation within each lineage could be accounted for by nonsynonymous point mutation, indicative of balancing selection. The FST values for both coho (0.11) and chinook (0.13) salmon indicated that much of the allelic diversity was partitioned among populations. Neighbor-joining analyses of A1 allelic frequencies among coho and chinook salmon populations showed strong patterns of geographic differentiation similar to those based on neutral genetic markers such as microsatellite loci. Both natural selection and the salmonid zoogeographic history of frequent population bottlenecks have shaped the patterns of diversity observed at this and other Mhc exons in Pacific salmonids.

Alleles↗
PubMed2005

Phylogeography and population structure of Aedes aegypti in Arizona.

Aedes aegypti, the mosquito responsible for transmitting dengue, has colonized many cities and towns throughout Arizona. Determining both the migration between, and the origin of, local Ae. aegypti populations is important for vector control and disease prevention purposes. Amplified fragment length polymorphism was used to infer geographic structure and local substructure, and effective migration rates (M, migrants per generation) between populations, and to determine genetic differentiation between populations (PhiPT). Three geographically and genetically differentiated groups of populations were identified. Population substructure was only detected in the border town of Nogales. Reliable estimates of M between regions ranged from 1.02 to 3.41 and between cities within regions from 1.66 to 4.44. In general, pairwise PhiPT were lowest between cities within regions. The observed patterns of genetic differentiation suggest infrequent migration between populations and are compatible with the idea of human transport facilitating dispersal between regions.

Aedes↗
PubMedDate not supplied

Population structure and admixture in Cerro Largo, Uruguay, based on blood markers and mitochondrial DNA polymorphisms.

Recent studies of the Uruguayan population revealed different amounts of Amerindian and African genetic contributions. Our previous analysis of Afro-Uruguayans from the capital city of the Department of Cerro Largo showed a high proportion of African genes, and the effects of directional mating involving Amerindian women. In this paper, we extended the analysis to a sample of more than 100 individuals representing a random sample of the population of the whole Department. Based on 18 autosomal markers and one X-linked marker, we estimated 82% European, 8% Amerindian, and 10% African contributions to their ancestry, while from seven mitochondrial DNA site-specific polymorphic markers and sequences of hypervariable segment I, we determined 49% European, 30% Amerindian, and 21% African maternal contributions. Directional matings between Amerindian women and European men were detected, but differences involving Africans were not significant. Data about the specific origins of maternal lineages were also provided, and placed in a historical context.

Black People↗
PubMed1990

The effects of population structure on the spread of the HIV infection.

A model for the spread of human immunodeficiency virus (HIV) in a population of male homosexuals is presented. The population is divided into five groups on the basis of degree of sexual activity. Within each group, the individuals are classified as 1) susceptible; 2) infective; or 3) removed because of a lack of sexual activity associated with advanced acquired immunodeficiency disease (AIDS). The infective individuals are further subdivided into four stages of infection. Analyses of the model address two questions with regard to the spread of HIV: (1) What is the effect of level of sexual activity on an individual's risk for infection, and (2) What is the effect that assumptions about mixing between groups have on both individual risk and transmission throughout a population? Results from analyses using a number of different parameter estimates show that increased levels of sexual activity increase the likelihood that an individual will become infected. In addition, the initial spread of the disease is markedly affected by variation in the amount of contact among individuals from different subpopulations. The steady-state incidence of the disease is not markedly affected by variation in the contact patterns, but the size of the steady-state population and therefore the proportion of infected individuals in the population does vary significantly with changes in the degree of mixing among subpopulations. These results show clearly the sensitivity of model outcomes to variation in the patterns of contact among individuals and the need for better data on such interactions to aid in understanding and predicting the spread of HIV.

HIV Infections↗
PubMed1985

Selection for weaning weight and postweaning gain in Hereford cattle. I. Population structure and selection applied.

Single trait selection was practiced in three lines of Hereford cattle derived from a common base population. Selection was practiced on males only within sire families for increased weaning weight (WW) in the WW line (WWL), for postweaning gain (PG) in the PG line (PGL) and at random in the control line (CTL). Females were culled on the basis of age or reproductive failure. Progeny of selected bulls were produced in two herds from 1970 through 1981. The data consisted of records on 2,467 progeny of 125 sires and 922 dams. Generations of selection to produce the 1981 calf crop were 1.96, 1.85 and 1.80 for WWL, PGL and CTL, respectively. For calves born in 1981, mean cumulative selection differentials (CSD) were 54.5 kg in WWL and 37.8 kg in PGL. Corresponding values in standard deviation units (SDU) were 2.31 and 1.68, respectively. Secondary selection differentials were 25 to 40% as large as selection differentials for the primary traits. Unintentional selection in the CTL in 1981 was 16.2 kg or .68 SDU for WW and .2 kg or .01 SDU for PG, respectively. Regressions of CSD on year were 4.1 kg or .17 SDU in WWL and 3.2 kg or .14 SDU in PGL. Realized selection differentials were approximately 88% of the potential selection differentials in both lines. Inbreeding coefficients of dam and calves in 1981 were 2.0 and 3.5% in WWL, 2.1 and 3.5% in PGL and 2.9 and 5.8% in CTL.

Animals↗
PubMed2003

The effect of seasonal harvesting on stage-structured population models.

In most models of population dynamics, increases in population due to birth are assumed to be time-independent, but many species reproduce only during a single period of the year. We propose an exploited single-species model with stage structure for the dynamics in a fish population for which births occur in a single pulse once per time period. Since birth pulse populations are often characterized with a discrete time dynamical system determined by its Poincaré map, we explore the consequences of harvest timing to equilibrium population sizes under seasonal dependence and obtain threshold conditions for their stability, and show that the timing of harvesting has a strong impact on the persistence of the fish population, on the volume of mature fish stock and on the maximum annual-sustainable yield. Moreover, our results imply that the population can sustain much higher harvest rates if the mature fish is removed as early in the season (after the birth pulse) as possible. Further, the effects of harvesting effort and harvest timing on the dynamical complexity are also investigated. Bifurcation diagrams are constructed with the birth rate (or harvesting effort or harvest timing) as the bifurcation parameter, and these are observed to display rich structure, including chaotic bands with periodic windows, pitch-fork and tangent bifurcations, non-unique dynamics (meaning that several attractors coexist) and attractor crisis. This suggests that birth pulse, in effect, provides a natural period or cyclicity that makes the dynamical behavior more complex.

Algorithms↗
PubMed1998

Population structure of Andean Triatoma infestans: allozyme frequencies and their epidemiological relevance.

Triatoma infestans (Hemiptera: Reduviidae) from 22 Andean localities in Bolivia (n = 968) and Peru (n = 37) were analysed by multi-locus enzyme electrophoresis. Among 12 gene-enzyme systems analysed, GPD, 6GPD and PGM were polymorphic, ACON, G6PD, GPI, 1DH, LAP, MDH, ME, PEP-A and PEP-B were monomorphic. Allozyme frequencies were analysed in relation to geographical and climatic factors, and the presence or absence of Trypanosoma cruzi infection. At one locality (Vallegrande, Bolivia), the frequency of 6Pgd-1 was significantly higher in infected (41% of 85) than in uninfected (17% of 83) adult T. infestans, although no such difference was found among nymphs (n = 347). From other localities, only insects infected with T. cruzi were subjected to isozyme analysis. Populations of T. infestans within villages showed panmixia, while genetic differentiation of T. infestans between villages was correlated with the distance between them. The genetic structure of T. infestans natural populations followed an 'isolation by distance' model, involving a series of founder effects followed by genetic drift, rather than adaptation in response to differential selection pressures. This conforms with circumstantial evidence that T. infestans spread, mainly in association with recent human migrations, from a source, probably in southern Bolivia. Isoenzyme characterization of populations of T. infestans could be used to infer sources of re-infestation during the surveillance phase of control programs.

Animals↗
PubMed2006

Genetic population structure and call variation in a passerine bird, the satin bowerbird, Ptilonorhynchus violaceus.

Geographic variation in vocalizations is widespread in passerine birds, but its origins and maintenance remain unclear. One hypothesis to explain this variation is that it is associated with geographic isolation among populations and therefore should follow a vicariant pattern similar to that typically found in neutral genetic markers. Alternatively, if environmental selection strongly influences vocalizations, then genetic divergence and vocal divergence may be disassociated. This study compared genetic divergence derived from 11 microsatellite markers with a metric of phenotypic divergence derived from male bower advertisement calls. Data were obtained from 16 populations throughout the entire distribution of the satin bowerbird, an Australian wet-forest-restricted passerine. There was no relationship between call divergence and genetic divergence, similar to most other studies on birds with learned vocalizations. Genetic divergence followed a vicariant model of evolution, with the differentiation of isolated populations and isolation-by-distance among continuous populations. Previous work on Ptilonorhynchus violaceus has shown that advertisement call structure is strongly influenced by the acoustic environment of different habitats. Divergence in vocalizations among genetically related populations in different habitats indicates that satin bowerbirds match their vocalizations to the environment in which they live, despite the homogenizing influence of gene flow. In combination with convergence of vocalizations among genetically divergent populations occurring in the same habitat, this shows the overriding importance that habitat-related selection can have on the establishment and maintenance of variation in vocalizations.

Animals↗
PubMed2005

Enterococci from Tolminc cheese: population structure, antibiotic susceptibility and incidence of virulence determinants.

Microbiological analysis of ripened artisanal Tolminc cheese revealed the presence of an enterococcal population in numbers of up to 10(6) per g. All colonies, isolated from the citrate azide tween carbonate (CATC) enterococcal selective medium were Gram positive and coccal-shaped and were analysed with PhenePlate FS system. This system discriminated 10 PhP clusters among the 90 enterococcal isolates. From each cluster the most representative isolate for that particular type was selected for further study. The 10 representative enterococci were catalase negative and grew in the presence of NaCl (2%, 4% and 6.5%) and bile salts (0.06%). Genus specific primers confirmed all 10 enterococcal representatives as Enterococcus members, while species specific primers determined them further as strains of Enterococcus faecalis species. PCR for vanA and vanB genes detection, respectively, amplified no PCR products. The absence of van genes was confirmed with both disc and E-test, as isolates were susceptible to vancomycin according to the National Committee for Clinical Laboratory Standards (NCCLS). The results of disc tests with other antimicrobial agents (ampicillin, vancomycin, kanamycin, penicillin, erythromycin, neomycin, chloramphenicol, clindamycin, rifampin) did not differ much among the tested enterococci: they were all very resistant to clindamycin only. The incidence of enterococcus virulence determinants was as expected: all of the 10 E. faecalis strains tested possessed multiple determinants (between 7 and 11).

Anti-Bacterial Agents↗
PubMed2001

Parasite (Schistosoma mansoni) and host (Biomphalaria glabrata) genetic diversity: population structure in a fragmented landscape.

Random amplified polymorphic DNA (RAPD) markers were used to quantify genetic diversity within and between 5 populations of Schistosoma mansoni within its definitive host (Rattus rattus) and the 5 corresponding populations of the snail intermediate host (Biomphalaria glabrata) from a limited endemic area of murine schistosomiasis on the island of Guadeloupe. Analysis of molecular variance (AMOVA) and canonical correspondence analysis (CCA) were used to test the significance of genetic differentiation between populations. Both methods gave similar results. Of total gene diversity, 15.1% (AMOVA) and 18.8% (CCA) was partitioned between localities for S. mansoni with an absence of association between genetic and geographical distances. Geographical localities accounted for 20.5% (CCA) of the total diversity for B. glabrata populations. The genetic distances between pairs of parasite populations were not correlated with the genetic distances between the corresponding pairs of snail host populations. Such strong patterns of local differentiation of both parasite and snail populations are consistent with predictions based on metapopulation dynamics and may have implications on host-parasite susceptibility relationship through local adaptation processes.

Animals↗
PubMed2005

Aedes aegypti (L.) and Aedes polynesiensis Marks (Diptera: Culicidae) in Moorea, French Polynesia: a study of adult population structures and pathogen (Wuchereria bancrofti and Dirofilaria immitis) infection rates to indicate regional and seasonal epidemiological risk for dengue and filariasis.

Populations of Aedes aegypti (L.) and Aedes polynesiensis (Marks) on Moorea Island, French Polynesia, the local vectors of dengue and filariasis, respectively, were sampled by landing/biting collection at nine localities on the east, north, and west coasts, during the late dry season, early and late wet season (September-May) 2003 and 2004, to investigate epidemiologically important features of the populations and compare them between regions and months. Biting rates of both species tended to increase (but not always significantly) for each species in each region each month from the late dry season to the late wet season, and the north coast region had significantly higher biting rates of Ae. aegypti. Insemination rates of Ae. polynesiensis females (94.5-98.8%) were consistently greater than those of Ae. aegypti (87.5-93.5%) throughout the study, but there was no significant difference in the insemination rates of either species between months and regions. Parity rates were generally highest in north coast samples and lowest in west coast samples for both species and generally increased (albeit not always significantly) by month for each species, with a range of 52.9-88.8% for Ae. polynesiensis and 28.6-53.6% for Ae. aegypti, although the high gravid rate (15.8-45.9%) of Ae. aegypti samples (reflecting its feeding more than once in a gonotrophic cycle) confounded both intraspecific and interspecific comparisons. Filarial infection was rare in Ae. aegypti, although both W. bancrofti and D. immitis were recorded, and infection rates in Ae. polynesiensis increased through the study period in each region for both filarias, with up to 4.6% infected and 1.4% infective for W. bancrofti and up to 6.3% infected and 2.5% infective for D. immitis. For W. bancrofti, infection rates were significantly lower on the west coast and also in the dry season, whereas rates for infective stages were significantly greater in the late wet season. For D. immitis there was no significant difference in infection rates between regions, but rates were significantly greater in the late wet season. Rainfall in all months sustains populations of both vectors and explains the relatively few significant differences between seasons; however, the wet season may provide for increased vector abundance and longevity, and present a potentially increased risk for transmission. Although the differences shown between regions also were limited in a statistical sense, there were increased risks for the northern and eastern regions, where both locals and tourists are concentrated and where the seaports and airport are located, and these areas should be priority targets for disease surveillance and vector control.

Aedes↗